1. Field of the Invention
The present invention relates to methods of stringing electrical conductors in bundles from suspension brackets.
2. Description of the Prior Art
In high voltage transmission lines, it is common practice to suspend sub-conductors or cables in a bundle from a tower by means of a suspension assembly comprising a suspension bracket or yoke suspended at the lower ends of insulator strings, which are connected at their upper ends to a cross-arm of the tower.
To provide such a suspension of the cables, the suspension bracket is firstly suspended from the tower by the insulator strings, and a bundle or stringing block is suspended from the suspension bracket, the bundle or stringing block comprising a plurality of rollers or pulleys formed with peripheral grooves for receiving the cables.
In some cases, the bundle block may be supported directly from the tower cross-arm independently of the suspension bracket and insulator strings.
A pulling line is passed through the bundle block, and the bundle of cables is pulled into place using a common pulling board.
The cables are then "sagged" to the correct tension, after which the cables are "clipped in", i.e. transferred from the bundle or stringing block to the suspension bracket, to which they are attached by clamps. The transfer of the cables from the bundle or stringing block to the suspension bracket is effected by temporarily supporting the cables to remove their weight from the bundle or stringing block, the cables usually being supported by cushioned support brackets attached to the cables, and the support brackets being connected to the tower cross-arm, usually by means of a coupling yoke and an adjustable system to permit raising of the cables from the bundle block. The block is then normally removed to enable the cables to be transferred to their final positions in suspension clamps provided on the suspension bracket.
It is also usual to temporarily support at least one of the cables from the suspension bracket before removal of the stringing block in order to tension the insulator strings.
It has been known for some time that the cable suspension should desirably be designed so as to avoid the existence of undesirably high voltage gradients across the individual insulators of the insulator strings by which the suspension bracket is suspended. Devices such as grading rings and shields have been employed in the past in order to make such voltage gradients more uniform and thereby to relieve stress across the insulators situated nearest the suspension bracket, which would otherwise bear disproportionately high fractions of the total line to ground voltage.
Also, it has been proposed to design the suspension bracket to counteract such high voltage gradients by supporting the cables near the lowermost insulators of the strings.
For example, in Canadian Pat. No. 653,027, issued Nov. 27, 1972, inventor Robert G. Baird there is disclosed a suspension bracket for supporting the tension cables, the bracket being constructed so as to support at least one of the cables generally outwardly and approximate the lowermost few of the insulators of insulator strings suspending the bracket.
Also, the U.S. Pat. No. 3,076,863, issued Feb. 5, 1963 to A. D. Lantz et al., there is disclosed an arrangement of conductor cables including a suspension bracket or plate having two arms extending equally and oppositely from the body of the suspension plate in the transverse direction and equally in the direction of the suspension insulators, so that the two top cables are disposed closely adjacent the adjacent one of the suspension insulators.
In addition, in order to keep to a minimum the required height of the towers required for suspending the cables, it is desirable to have the bundle of cables positioned as high as possible with respect to the suspension bracket. This can advantageously be done by clamping one or more of the cables to the top of the suspension bracket, and the aforementioned U.S. Pat. No. 3,076,863 for example, discloses an arrangement in which three cables are clamped to a suspension plate in a triangular array with one of the cables, at the apex of the triangular array, positioned near the top of the suspension bracket and between two strings of insulators disposed in a V-array.
However, this previously proposed arrangement has hitherto presented a problem in that no practical and suitable method has been developed for "clipping in" the uppermost cable during the cable bundle stringing operation.